1. Field of the Invention
The present invention relates to a speed control apparatus of a working vehicle such as a vehicle for a construction, civil engineering work and the like, which is provided with a crane function, and a speed control method thereof. More particularly, it relates to a speed control apparatus of a working vehicle which can adjust a working speed of a working machine and a traveling speed of the vehicle within a predetermined speed range under a crane mode so as to improve a working efficiency, and a speed control method thereof.
2. Description of the Related Art
A working vehicle for various kinds of construction, civil engineering machines and the like is provided with a working machine comprising a revolving frame mounted onto an undercarriage so as to freely revolve around a vertical axis, and a main boom, a stick boom, a bucket, a suspending hook and the like mounted on the revolving frame. A discharged pressure oil supplied from a variable delivery pump is supplied to a main boom cylinder, a stick boom cylinder, a bucket cylinder, a revolving motor, a traveling motor and the like, whereby the working vehicle drives or travels each of the working machines.
An example of the working vehicle mounted with such actuators is disclosed, for example, in Japanese Patent No. 2863599. A hydraulic working machine as disclosed in the publication is provided with an accelerator lever for setting an engine speed, an engine-speed command transmitting device for detecting an amount of operation of the accelerator lever so as to output an engine speed command signal in correspondence to the amount of the operation, engine speed setting means for increasing and reducing the engine speed, flow amount adjusting means for increasing and reducing a pump flow amount of a variable delivery pump, a relief valve for setting a maximum operating pressure in a discharge side of the pump, and relief pressure setting means for setting a maximum pressure of a pressure oil introduced to actuators for a working machine.
Further, the hydraulic working machine is provided with working mode selecting means, which previously stores various kinds of working modes such as a working mode for working the actuators at a high speed, a working mode for executing a precise work and the like, in addition to a combination of an application force and a working speed of the actuators required for a normal work, in order to freely select the working mode.
When an operator selects a desired working mode by the working mode selecting means in correspondence to working contents and working conditions to be executed, the working mode selecting means selects at least one of a maximum engine speed, a maximum discharge flow amount of the pump and a maximum pressure of the pressure oil introduced to the working machine actuators, which are previously stored for each selected working mode, and outputs as a working mode command signal to a controller.
The controller receives the working mode command signal from the working mode selecting means and the engine speed command signal from the engine speed command transmitting device, and suitably selects the maximum engine speed among the working mode command signal and the engine speed command signal so as to output the command signal to the engine speed setting means. At the same time, the controller outputs the command signal to the pump flow amount adjusting means on the basis of the working mode command signal, and outputs the command signal to the relief valve and the relief pressure setting means.
In the manner as mentioned above, the controller outputs the command signal to the flow amount adjusting means and the engine speed setting means such that the working speed of the actuators operated on the basis of the command signal output from the controller is neither too much nor too little, thereby controlling the discharge oil amount of the variable delivery pump. At the same time, the controller outputs the command signal to the relief valve and the relief pressure setting means so that a working force of the actuator is neither too much nor too little, thereby controlling the pressure of the pressure oil flowing into the actuator.
In accordance with the conventional hydraulic working vehicle, the flow amount and the maximum pressure of the pressure oil flowing into the actuators are automatically restricted by the engine speed setting means, the flow amount adjusting means, the relief pressure setting means and the like. Accordingly, it is possible to obtain the working speed and the application force, which are optimum for the working contents and the working conditions of the selected working mode.
On the other hand, in this kind of working vehicle, a working speed of a main boom cylinder and a stick boom cylinder at the time of normal excavating operation, a dumping operation or the like is set such that, for example, a speed at the time of ascending the main boom and the stick boom is about 30% of a speed at the time of descending them. This can be applied in the same manner even to a hydraulic working vehicle having a crane function, in which a suspending hook is mounted to a stick boom front end portion of a normal working vehicle. Even when it is switched to a crane mode, an ascending speed of a peripheral portion of the suspending hook is widely delayed in comparison with a descending speed thereof.
The hydraulic working machine disclosed in the patent publication mentioned above previously expects various kinds of preferable working modes corresponding to various kinds of driving and operating conditions, and stores them in the working mode selecting means. However, these working modes are selected by the operator himself on the basis of his/her sense and judgement with respect to environmental conditions immediately before starting the operation, even when the working contents and the working conditions have changed. For example, under a condition that various environments such as a change in the weather, a change in the working range, with or without an obstacle and the like are generated, an operation of the set working mode does not always coincide with an actually executed working condition.
The controller only uniformly outputs the command signal corresponding to the set working mode to the engine, the variable delivery pump, the relief valve and the like. Thus, once a certain mode is set, it is impossible to change the set working speed and the set working pressure of the working machine in the working mode, even in the case that a change has been generated in the executed working contents or the working conditions. Accordingly, in the case that the preset working mode does not comply with the actual working condition, or in the case that it is not a mode that can correspond to a skill of the operator, the operation has to be executed within the working mode range. Therefore, a working efficiency or the like is easily reduced.
In particular, in the working vehicle provided with the crane function, since the operation is executed in a state that the descending speed of the periphery of the suspending hook and the ascending speed thereof are widely different from each other, as in the same manner as that at the normal excavating time as mentioned above, even when it is switched to the crane working mode. Therefore, the operator who operates the crane within a cab can not be used to the speed difference, so that he/she can hardly expect the switching timing between the ascending operation of the suspended load and the descending operation thereof, whereby a working efficiency is going to be reduced.
The present invention is made in order to solve the conventional problems. An object of the present invention is to provide a speed control apparatus of a working vehicle which can reduce a working speed of a working machine and a traveling speed of a vehicle to a desired speed range in correspondence to a change of working contents and working conditions at the time of executing a crane operation on the basis of a preset crane mode, thereby improving a working efficiency or the like, and to provide a speed control method thereof.
In accordance with a first aspect of the present invention, there is provided a speed control apparatus of a working vehicle for controlling a working speed of each actuator at the time of being in a crane mode, comprising: setting means for a maximum engine speed to be set at the time of being switched to the crane mode; setting means for a proper pump absorbing torque curve at the time of being switched to the crane mode; setting means for setting a pump discharge amount introduced from an intersecting point of an engine speed torque curve at the maximum engine speed with the proper pump absorbing toque curve to be an upper limit; setting means for an optional pump absorbing torque curve being within a range of the engine speed torque curve and capable of obtaining an optional pump discharge amount which is smaller than the pump discharge amount set as the upper limit and which is larger than the pump discharge amount introduced from the pump absorbing torque in correspondence to a minimum engine speed at the time of being in the crane mode; and setting means for setting a swash plate angle in correspondence to a change of the pump absorbing torque.
In accordance with the first aspect of the present invention, when being switched to the crane mode, a signal for reducing to a preset engine speed is output from a controller. The engine speed at this time corresponds to the largest engine speed required at the time of a crane operation. Accordingly, the controller previously stores such information as an engine speed torque curve, a minimum engine speed required for the working vehicle, a proper pump absorbing torque at the time of being in the crane mode operation, and the like. A pump absorbing torque curve in correspondence to each of the engine speeds is calculated on the basis of a control program at the time of selecting the crane mode, in the speed range of the maximum engine speed set at the time of being switched to the crane mode and the minimum engine speed required for the working vehicle.
That is, the pump discharge amount introduced from the pump absorbing torque at the intersecting point of the engine speed torque curve in correspondence to the maximum engine speed with the pump absorbing torque curve within the engine speed range is set to be an upper limit value thereof. The pump absorbing torque curve is set by connecting that upper limit value with the pump discharge amount introduced from the proper pump absorbing torque in correspondence to the minimum engine speed required for the working vehicle at an optional point. In this case, however, it is necessary that the value of the pump absorbing torque in correspondence to each of the engine speeds, which is optionally selected at this time, should be within the range surrounded by the engine speed torque curve.
When the operator has selected the crane mode, the engine speed is automatically reduced to a predetermined engine speed. At the same time, the swash plate angle is changed on the basis of the command from the controller so as to become the pump discharge amount corresponding to the upper limit value previously set. At the time of being in the crane mode, when the operator further adjusts the working speed of the crane, the swash plate angle is automatically controlled to the pump absorbing torque corresponding to the working speed of the crane, for example, along the above-mentioned optional pump absorbing torque curve set between the maximum engine speed and the minimum engine speed. That is, the working speed of the actuators, the driving speed of the traveling motor and the like in the current crane mode are expanded within the pump absorbing torque range between the upper limit value and the lower limit value of the pump discharge amount.
In the manner mentioned above, even under various environments such as the change of the working range, with or without the obstacle and the like, it is possible to effectively obtain an optimum crane mode corresponding to the executed working contents, the working conditions, the skill of the operator and the like, so that not only it is possible to realize a stable traveling property of a vehicle and an operability of the working machine, but also it is possible to significantly improve an operation efficiency and the like.
Further, in accordance with the first aspect of the present invention, it is preferable that the speed control apparatus further comprises pilot pressure adjusting means in a side of a pilot pressure receiving chamber for supplying a hydraulic pressure of a main valve that distributes a working fluid to a main boom cylinder, a hydraulic motor and the like, wherein an opening area of the main valve is adjusted by the pilot pressure adjusting means.
For example, in the main boom cylinder, the main boom is operated in a stand-up direction thereof in accordance with an extending motion of the main boom cylinder and is operated in a tilt-down direction in accordance with a contracting motion thereof. However, since a position of a center of gravity of the main boom exists at a front portion of the upperstructure, a force in a contracting direction for tilting down the main boom is applied to the main boom cylinder due to a weight of the suspended load or the like. When the main boom is tilted down at the time of operation of the crane, it is impossible to slow the tilt-down speed of the main boom only by controlling the pump flow amount.
In accordance with the first aspect of the invention, the upper limit of the maximum speed at the time of tilting down the main boom is set by controlling the supply of the pilot pressure oil by the pilot pressure adjusting means. The tilt-down speed of the main boom is slowed by adjusting a stroke of the spool of the main valve within the speed range having the main boom tilt-down speed as the upper limit and making it smaller than the opening area of the normal spool to reduce the flow amount of the pressure oil supplied to the main boom cylinder head side. As mentioned above, it is possible to further make the tilt-down speed of the main boom slower than the speed of the normal crane mode, so that an operability of the crane executed by the operator is improved.
Furthermore, in accordance with the first aspect of the present invention, it is preferable that an opening area of the main valve for distributing working fluid to an actuator such as a main boom cylinder and the like at the time of being in the crane mode is set such that a descending speed of a peripheral portion of a suspending hook mounted to a front end side of a stick boom is reduced to be substantially equal to an ascending speed thereof.
In the conventional working vehicle provided with a crane function, even when being switched to the crane mode, a great difference exists between the ascending speed and the descending speed of the peripheral portion of the suspending hook, that is, the ascending speed and the descending speed at the time when the main boom and the stick boom swing, in the same manner as the normal working mode as mentioned above. Thus, the descending speed is widely larger than the ascending speed, so that the operator can not easily grasp the speed difference. Therefore, it is hard to estimate the switching timing for ascending and descending the suspended load, and a great influence bears on the working efficiency.
Then, in accordance with the first aspect of the present invention, the structure is made such that when being switched to the crane mode, it is possible to automatically or intentionally adjust the opening area in the descending side of the main valve for the main boom and/or the stick boom to be substantially equal to the opening area in the ascending side thereof. This adjustment can be executed, for example, by using the pilot pressure adjusting means as mentioned above. As the pilot pressure adjusting means, there is a simple pressure reducing valve besides an electric hydraulic control valve, which will be mentioned in an embodiment of the present invention.
The electric hydraulic control valve is so structured that when a signal responding to an operation amount executed by the crane mode switch at the time of operating the crane is input to the electric hydraulic control valve via the controller, a throttle area of the electric hydraulic control valve set in correspondence to an input amount is controlled within a range of a set speed of the main boom at the time of being in the crane mode. That is, it is possible to finely adjust a flow amount of the pressure oil supplied from the descending side of the main valve to the main boom cylinder and/or the stick boom cylinder so as to be substantially equal to a flow amount of the pressure oil supplied to the ascending side of each of the cylinders via the main valve, within the speed range at the time of being in the crane mode. Further, in the case of using the electric hydraulic control valve, the speed set mentioned above can be achieved even in the case of inputting to the electric hydraulic control valve via an independent signal output system without directly connecting to the controller mentioned above. Thus, it is possible to adjust a flow amount on the spot on the basis of the conditions of the working field.
On the other hand, in the case that it is not required to finely adjust in the working field, it is preferable to use a pressure reducing valve for the pilot pressure adjusting means. In this case, the pressure oil supplied to the pilot pressure receiving chamber in the descending side of the main valve is pressure reduced to the preset pressure via the pressure reducing valve, and the opening area of the main valve is adjusted such that the flow amount of the pressure oil supplied from the descending side of the main valve with respect to the main boom cylinder and/or the stick boom cylinder becomes substantially equal to the flow amount of the pressure oil supplied to the ascending side of each of the cylinders via the main valve.
In the manner as mentioned above, when being switched to the crane mode from the normal working mode, it is possible to automatically or intentionally adjust the descending speed of the main boom and/or the stick boom so as to be substantially equal to the ascending speed thereof. Therefore, the operator can smoothly execute the crane operation, whereby an operation efficiency can be improved.
In accordance with a second aspect of the present invention, there is provided a speed control apparatus of a working vehicle having control means for controlling a speed of a hydraulic motor at the time of being in the crane mode, including: fixing means for maintaining a tilt and rotation angle of the hydraulic motor in a larger side thereof so as to be fixed to a low speed side at the time of being switched to the crane mode.
In accordance with the second aspect of this invention, at the time of being switched to the crane mode, the tilt and rotation angle of the hydraulic motor is maintained in the larger side and the hydraulic motor is rotated at a low speed by operation of the fixing means, for example, having a cut valve for freely supplying and shutting, or the like. An upper limit of a maximum speed of the hydraulic motor is set. The speed is adjusted within the speed range having this upper limit speed, and the speed of the hydraulic motor is locked in a low speed side without being affected by the stroke of the spool of the main valve. Since the upper limit of the maximum speed of the hydraulic motor is set in the manner as mentioned above, it is possible the travelling and revolving are smoothly performed at the time of the operation of the crane.
A working speed control method of various kinds of actuators in a working vehicle in accordance with a third aspect of the present invention can be executed by using the speed control apparatus as mentioned above. According to a typical method of the present invention, there is provided a speed control method of a working vehicle controlling a working speed of each of actuators at the time of being in a crane mode, comprising steps of: setting a maximum engine speed at the time of being switched to the crane mode; setting a proper pump absorbing torque curve at the time of being switched to the crane mode; setting a pump discharge amount introduced from an intersecting point of an engine speed torque curve at the maximum engine speed with the proper pump absorbing toque curve to be as an upper limit; setting an optional pump absorbing torque curve being within a range of the engine speed torque curve and capable of obtaining an optional pump discharge amount which is smaller than the pump discharge amount set as the upper limit and which is larger than the pump discharge amount in correspondence to a minimum engine speed at the time of being the crane mode; and setting a swash plate angle in correspondence to a change of the pump absorbing torque.
In accordance with the third aspect of this invention, when the operator selects the crane mode, the controller sets the pump discharge amount at the intersecting point between the engine speed torque curve at the predetermined maximum engine speed and the proper pump absorbing torque curve previously set on the basis of the calculation to be as the upper limit value as mentioned above. There is set the optional pump absorbing torque curve obtained by connecting the upper limit value with the pump discharge amount in correspondence to the pump absorbing torque required in correspondence to the predetermined minimum engine speed required for the working vehicle.
In the case that it is intended to restrict the working speed to a low level in correspondence to the change of the work contents and the working conditions, the skill of the operator or the like when the crane operation is executed on the basis of the set crane mode, the operator selectively operates, for example, a speed adjusting switch (an engine speed dial) so that the engine speed is set along the optional pump absorbing torque curve set between the maximum engine speed and the minimum required engine speed on the basis of the output signal of the speed adjusting switch and the swash plate angle is set on the basis of the pump absorbing torque in correspondence to the engine speed.
It is possible to further reduce the engine speed, the pump discharge amount and the like in correspondence to the change of the work contents and the working condition, the skill of the operator or the like, and it is possible to adjust the working speed of the working machine cylinder, the driving speed of the traveling motor and the like at the time of being in the current crane mode to be an optional speed.
Further, in accordance with the third aspect of the present invention, it is preferable that the speed control method comprises a step of setting a descending speed of a periphery of a mounting portion of a suspending hook mounted to a front end side of the stick boom so as to be reduced to be substantially equal to an ascending speed thereof.
The speed set can be realized by using the pilot pressure adjusting means with respect to the main valve for the main boom and the stick boom as mentioned above. The descending speed of the periphery of the mounting portion of the suspending hook onto the front end side of the stick boom is reduced so as to be substantially equal to the ascending speed thereof, in such a manner that the opening area of the descending side of the main valve becomes substantially equal to the opening area of the ascending side thereof, only at the time of being in the crane mode. As mentioned above, since the speed is reduced so as to become substantially equal to the ascending speed which is inherently set to be widely lower than the descending speed, it is possible to smoothly execute a further operation and it is possible to achieve an efficiency of the operation.